1. Field of the Invention
The present invention relates to a photosensitive transfer material, and, particularly to a photosensitive transfer material in which a temporary support and a photosensitive layer can be completely separated and to a color filter using the photosensitive transfer material.
2. Description of the Related Art
Photosensitive transfer materials whose photosensitive resin layer is transferred to a substrate are used in print wiring, intaglio printing and relief printing and for making nameplates, multicolor trial printing print samples, offset printing plates and color filters.
The photosensitive transfer material usually comprises a support, an intermediate layer (peelable layer) or an intermediate layer and an alkali-soluble thermoplastic resin layer, and a photosensitive resin layer. When forming an image on a substrate, the formation is made by overlapping a separately prepared substrate on the photosensitive resin layer of the photosensitive transfer material, thereafter peeling off only the (temporary) support, exposing the photosensitive resin layer imagewise through the intermediate layer and developing the image.
The aforementioned intermediate layer is an oxygen-blocking layer, whereby polymerization of the photosensitive resin layer by exposure can be carried out even when in contact with air without suffering any polymerization inhibition due to oxygen. Because the intermediate layer is thin (about 0.5 to 5 xcexcm), it does not adversely affect resolution. The irregularities of a base (namely, irregularities due to pixels that have already been formed) can be absorbed by the alkali-soluble thermoplastic resin layer. These layers are alkali-soluble and are therefore removable when developing.
One such example includes color filters used in color liquid crystal displays. These generally have a fundamental structure in which each pixel of R, G and B (red, green and blue) is formed and a black matrix (K) for improving display contrast is formed in the space between each pixel.
As to the method of forming a color filter, these layers (the alkali-soluble thermoplastic resin layer, intermediate layer and photosensitive resin layer) are transferred to the surface of the color filter substrate by using the above-described transfer material. Next, the temporary support is peeled off and exposure using a predetermined mask and developing using an alkali to form a pattern are carried out. It is essential that each of these R, G and B pixels of the color filter and the surface of K be very smooth.
Problems often occur during high-speed transfer of the photosensitive transfer material. Namely, a part of the alkali-soluble thermoplastic resin layer may remain on the temporary support when peeling off the temporary support and it is impossible to separate completely the temporary support and the alkali-soluble thermoplastic resin layer. Therefore, it is often the case that acceptable smoothness cannot be obtained during exposure because of the surface irregularities in the alkali-soluble thermoplastic resin layer.
A method is described in Japanese Patent Application No. 3-120228 for peeling the interface other than that between the thermoplastic resin layer and the temporary support. This method uses a photosensitive transfer material prepared by disposing a thermoplastic resin layer, a peelable layer and a photosensitive resin layer in this order on a temporary support, especially, a plastic film undercoated with a gelatin, where the photosensitive resin layer is bonded to a substrate and then the temporary support and the thermoplastic resin layer are peeled and removed simultaneously so as to transfer the photosensitive resin layer to the substrate. However, in this method, it is extremely difficult to control the peelability of the peelable layer from the thermoplastic resin layer and is, from an automated peeling operation standpoint, far from satisfactory.
The object of the present invention is to solve the aforementioned prior art problem and to provide a photosensitive transfer material in which an alkali-soluble thermoplastic resin layer and a temporary support can be completely separated without a part of the alkali-soluble thermoplastic resin layer remaining on the temporary support even if a photosensitive transfer material is transferred at a high speed and also to provide a color filter using the photosensitive transfer material.
The invention has been completed as a result of the intensive studies made by the inventors and concerning interfacial peelability.
A first aspect of the invention provides a photosensitive transfer material comprising a temporary support, a peelable layer, an alkali-soluble thermoplastic resin layer, an intermediate layer and a photosensitive resin layer that are disposed in this order, wherein the bonding strength between the peelable layer and the thermoplastic resin layer is the smallest of all the bonding strengths between neighboring layers.
The provision of the peelable layer between the temporary support and thermoplastic resin of the photosensitive transfer material makes it possible to obtain a photosensitive transfer material in which the thermoplastic resin and the temporary support can be completely separated when peeling off the temporary support even if the photosensitive transfer material is transferred at a high speed.
Also, a second aspect of the invention provides a color filter formed using the above-mentioned photosensitive transfer material.